The present invention relates to a method and appartus for optically aligning solid-state imagers.
When a plurality of solid-state imagers are optically arranged to view the same image and each imager is to supply an electrical signal which is a component part of the image, it is necessary that the photosensitive imagers. For example, in a color video camera, a color light-splitting prism can split the light reflected from a scene into its red (R), green (G) and blue (B) components. A solid-state imager can be positioned at a respective exit port of the prism for receiving a component color image of the scene and supplying a corresponding electrical signal. In order to properly reproduce the image in full color, it is necessary that the R, G, and B component electrical signals represent color components which spatially coincide with each other. That is, each of the solid-state imagers must be precisely registered with one another such that their respective electrical signals simultaneously refer to the same portion of the image.
In the prior art, such as U.S. Pat. No. 4,323,918 entitled OPTICAL ASSEMBLY FOR COLOR TELEVISION, issued Apr. 6, 1982 to Bendell, the individual solid-state imagers (each imager including a solid-state imaging chip housed in a ceramic insulating integrated circuit (IC) package are positioned at the respective prism exit ports using an adhesive which does not cure or harden until exposed to a given amount of ultraviolet (UV) light. Next, electrical connection is made to each imager and operating signals are applied in order that the imagers are operating correctly. The component color electrical signals from each imager are then simultaneously viewed on a video monitor. Next, each imager is repositioned on its respective prism exit port until each color raster spatially coincides with each other raster to within an acceptable tolerance, such that the image is correctly reproduced in full color. Finally, the imagers adhesives are exposed to UV light for curing the adhesive and fixing the imagers relative position on the prism. This alignment technique requires that temporary electrical connections be made to operate each of the imagers. This is undesirable since the operating levels for each imager may be different due to process variations. Consequently, this alignment technique is time consuming and requires a skilled operator, both of which increase the manufacturing cost of the completed camera.
In my copending U.S. patent application (RCA) 81,218) entitled SOLID-STATE IMAGER CHIP MOUNTING, filed on even date herewith and assigned, like the present application to RCA Corporation, I describe an imager mounting arrangement wherein unpackaged imager chips are directly bonded to respective exit ports of a prism. In a preferred embodiment, the photosensitive side of thinned substrate imager chips (i.e. imager chips wherein the substrate has been chemically etched to thin it to e.g. 8-10 micrometers) are bonded to the light exit ports of the prism. Bonding wires connect the chips bonding pads to a metallized conductor pattern on the prism exit face for providing electrical connections to the chip. Since bonding wires are fragile, it is desirable to fix the relative position of the imager chip on the prism exit port before the bonding wires are in place. Thus the temporary electrical connections for alignment are undesirable. Accordingly, there is a need for imager registration to be carried out without electrical operation of the imager chip.